1. Field of the Invention
The invention relates to a light source module for a scanning apparatus such as a bar code reader, and to a scanning apparatus with the light source module.
2. Description of the Related Art
Recently, point-of-sale systems (POS systems) have become common in stores. In a POS system, a bar code reader reads a bar code provided on an article. According to the POS system, check-out work is carried out only by scanning a beam emitted from a bar code reader. Thus, the work of an operator (salesclerk) is reduced by using a bar code reader.
A bar code reader generally includes a light source for emitting a beam, an arrangement for generating a scanning beam by reflecting the beam from the light source, such as a rotating polygon mirror, a plurality of mirrors for reflecting the scanning beam and for dividing the scanning beam to provide a set of scanning lines outside of the bar code reader. The return beams reflected by a bar code on an article are condensed by a concave mirror or a condenser lens onto a light receiving device, such as a photodiode which generates an electrical signal corresponding to the return beams received by the light receiving device. These elements are sealingly contained within a housing to provide an optical unit.
Such an apparatus for reading a bar code is a kind of a scanner apparatus, similar to a scanner device in a laser printer or a copy machine, and is often referred to as a POS scanner or a bar code scanner. A laser diode is often used as a light source because of its compactness, low power consumption, and cost while a gas laser beam (for example, He--Ne laser beam) was originally used.
A laser diode has a problem that its life is shorter than a gas laser so that a bar code reader with a laser diode must be designed and used while considering replacement of the light source. Further, there is a problem that static electricity may damage a semiconductor laser.
In the prior art, a light source is provided by a VLD (Visible Laser Diode) module which includes a laser beam source, a lens and an aperture for shaping a beam.
When replacing a laser diode, the VLD module is replaced with the laser diode. In the prior art, the VLD module is contained within the housing of the optical unit. Thus, the housing of the optical unit must be opened to replace the VLD module. This work must be carried out in a clean room to prevent dust, which may harmfully effect to the optical characteristics of the scanner, from entering the optical unit. There is also a problem that the bar code reader to be mended cannot be used during the replacement of the VLD module.